The present invention relates to a transmission for an automotive vehicle, and in particular relates to an automatic type transmission particularly suitable for use in a transverse front engine front wheel drive type automotive vehicle, or a so called FF vehicle.
There is a known type of front engine type front wheel drive type automotive vehicle in which the internal combustion engine thereof is mounted transversely to the vehicle body, with its crankshaft extending at right angles to the longitudinal axis of the automotive vehicle body, and in which the automatic transmission thereof is attached to the internal combustion engine with the directions of the rotational axes of the various mechanisms contained therein likewise extending transversely to the longitudinal axis of the vehicle body. In such a transverse type of construction, it is very important to keep the axial length of the automatic transmission as short as possible, so as to fit the transmission mechanism and the rotary power train of the vehicle as a whole into the shortest possible space, in view of the severe restriction imposed on the axial length of this rotary power train by the overall width of the vehicle, within which of course the rotary power train must be accomodated.
There is a per se well known form of transmission which has been evolved as suitable for such transverse mounting, in which a fluid torque converter is mounted to the internal combustion engine and is placed coaxially with said engine and with a gear transmission mechanism along a first axis and drives and gear transmission mechanism, and in which the rotary power output from said gear transmission mechanism is transferred sideways from said first axis to a lay shaft which extends along a second axis parallel to said first axis back under the gear transmission mechanism to a point approximately under the torque converter, where this engine side end of the lay shaft is rotationally connected to a differential device appropriate for a front wheel drive configuration.
This configuration of automatic transmission has been successfully implemented in the past, but owing to the limited space available along said first axis for providing said gear transmission mechanism the design process, manufacture, assembly, and servicing therefor have been rather difficult. Further, in line with the ever increasing requirements for smaller and smaller automotive vehicles, there has been recently a need to adapt these automatic transmissions to vehicles having even smaller widths than heretofore, which has been very difficult, in view of the problems in design, manufacture, assembly, and servicing outlined above.
Also, in the construction of such an automatic transmission, the compactness in the directions sideways from the axial direction described above which is transverse to the vehicle axis is important; in other words, it is important that the transmission not be too fat; and more particularly it is important that there not be too much of a bulge created by providing space within the transmission for accomodating the gear train which is necessarily provided for driving the above described lay shaft from the power output member of the gear transmission mechanism. The reduction of such a bulge, especially of the bulge at the lower side of the transmission around the end of the lay shaft, is important in view of the problem of interference between such a bulge and the drive shaft which drives the front wheel on that side of the automotive vehicle, which sometimes presents a problem.
Further, in the past, difficulties have been experienced with regard to making the transmission, and particularly the internal construction thereof, strong enough to be durable over a long period of time; in particular the lay shaft structure has experienced problems with regard to strength, which have affected its durability. The weight of the transmission as a whole, and the weight of the lay shaft structure in particular, also in some cases are critical design factors with regard to such a transmission. Finally, the question of noise produced by the gears in such a transmission, and in particular the question of the noise produced by the lay shaft asssembly, is important from the point of view of producing a transmission which is environmentally acceptable, as well as being easy and pleasant of operation by the driver of the vehicle, especially over a long period. This has importance with regard to questions of drivability of the vehicle as a whole. These questions of noise, and of durability, are related to the desire to simplify the bearing structure of such a lay shaft construction.
In order to meet with the abovementioned requirements, one of the present inventors has proposed an automatic transmission suitable for mounting in an automobile, for which inventive concept U.S. patent application Ser. No. 06/418,026 filed Sept. 14, 1982 has been filed, based upon Japanese Patent Application No. 147,436/81 filed on Sept. 17, 1981.
In this above indentified earlier proposal, a construction for an automatic transmission is suggested in which a fluid torque converter and a first gear transmission mechanism connected thereto are mounted along a first axial line, with a lay shaft extending along a second axial line which is parallel to said first axial line, and a second gear transmission mechanism is mounted on said lay shaft, with said lay shaft passing through said second gear transmission mechanism and being therefore a through lay shaft which rotationally supports said second gear transmission mechanism. A rotational power input member of the second gear transmission mechanism drivingly connected to a rotational power output member of the first gear transmission mechanism and a power output gear wheel of the automatic transmission are also supported by the through lay shaft so as to be rotatable about the second axial line. Thereby, the axial length of the entire construction is reduced, since the gear transmission mechanism is split into two parts which are arranged side by side with regard to the axial direction, and also the second gear transmission mechanism and the power output gear wheel which will drive a differential gear mechanism of the automobile to which the transmission is fitted are mounted securely and rigidly by the simple construction that they are supported on the through lay shaft. In further developments of the automatic transmission based upon the abovementioned basic concept, the present inventors have conceived the concept that the through lay shaft, which rotationally supports the second gear transmission mechanism, including the rotational power input member thereof as well as the power output gear wheel of the automatic transmission, i.e. the entire rotational members which rotate about said second axial line, should be also utilized as effectively as possible for transmitting rotational power along said second axial line.
Still further, in further developments of the automatic transmission based upon the aforementioned basic concept, it has also been conceived of by the present inventors that the through lay shaft extending along said second axial line through the entire rotational structure supported thereby should be effectively utilized to balance various axial thrust forces generated in various portions of the gear meshing mechanisms arranged along said second axial line. In fact, various axial thrusts are caused by axial pushing of the various gear wheels by the other gear wheels with which they are meshed, owing to the fact that these gear wheels are always formed as helically cut gear wheels, in view of the well known advantages of such a form of construction, such as smooth torque transmission, etc..